A different material welded joint and a welding method for joining an iron-based material (hereinafter, simply referred to as steel material) and an aluminum-based material (a collective term of pure aluminum and aluminum alloy, and hereinafter simply also referred to as aluminum material) having different melting points are disclosed in JP-B-4,438,691. This technology is to form a plurality of through-holes in the steel material at a joining place between the steel material and the aluminum material and to fill a filler material of the aluminum-based material in the through-holes, thereby performing welding. According to this technology, the filler material of the aluminum-based material is welded to the aluminum material serving as a matrix, and the filler material flooded onto a surface of the steel material from the through-holes upon the welding is cooled and then becomes welding beads, which are covered onto the steel material in the vicinity of the through-holes. Thereby, the steel material and the aluminum material, which are different materials, are joined.
However, according to the above technology of the related art, as the welding is progressed, an amount of input heat to a welded part increases, so that a melted amount of the filler material increases as the welding is progressed. In an extreme case, the aluminum material serving as a matrix may also be melted. That is, non-uniformity of a welding quality is caused between a welding start-side region and a welding end-side region. The reason is as follows: since the welding is continuously performed so that a welding line passes through respective central liens of the plurality of through-holes, in the above technology of the related art, welding heat is accumulated in the steel material and the aluminum material as the welding is progressed.